1. Field of the Invention
This invention relates to a soft magnetic alloy film to be suitably used for a magnetic head and it also relates to a magnetic head using such a soft magnetic alloy film for use in a magnetic recording apparatus such as a video cassette recorder.
2. Description of the Prior Art
In the field of magnetic recording technology, efforts have been made to enhance the coercive force of recording media such as magnetic tapes with a view towards improving the density of recording on the media. Such improvement requires developement of materials having a high saturated flux density (Bs) to be used as magnetic heads.
While Fe-Si-Al alloy (Sendust) has been popularly used as a soft magnetic material (film) having a high saturated flux density, noncrystal alloy films containing Cobalt (Co), a ferromagnetic metal, as a major ingredient have been developed in recent years.
More recently, films having a high saturated flux density and excellent soft magnetic characteristics have been developed by using finely crystallized alloys such as Fe-C and Fe-Si alloys to reduce the influence of the crystalline magnetic anisotropy of iron that can deteriorate the soft magnetism of the films.
A magnetic head of this type is required to have magnetic characteristics that can accommodate the high recording density of the magnetic recording medium as well as mechanical properties such as abrasion-resistivity and moldability.
An example of the magnetic heads that have been developed recently to meet these requirements is a composite type magnetic head (or a MIG head) produced by coating the surface of a ferrite substrate, a popular component of a magnetic head, with a soft magnetic material having a saturated flux density which is greater than that of the ferrite.
A composite type magnetic head normally has a configuration comprising a soft magnetic film as well as a gap between a pair of magnetic core halves made of ferrite and the components are bonded together by glass bonding.
In recent years, there has been a remarkable trend in the industry towards reducing the size and weight of electronic apparatus such as magnetic tape decks comprising magnetic heads, although the apparatus are often used under unfavorable conditions including vibration during transport. Thus, a magnetic head is required to have not only excellent magnetic characteristics and a high abrasion-resistivity but also outstanding durability in unfavorable environments where high temperature and corrosive atmosphere as well as vibration are dominant. To realize such durability, it is necessary to use a glass bonding technique for forming the gap and mounting the head into the casing. Consequently, the materials of the magnetic head and film are required to withstand the high temperature prevalent during the head manufacturing process.
Conventional soft magnetic alloy films which are made of Sendust normally have a saturated flux density of approximately 10,000G (Gauss), a value which is far from satisfactory for the current high density requirement. While amorphous alloy films that contain cobalt can have a high saturated flux density of more than 13,000G, any attempt to form an alloy with a high saturated flux density inevitably necessitates reduced levels of amorphousness inducing elements such as Ti, Zr, Hf, Nb, Ta, Mo, V and W, which in turn adversely affects the stability of the amorphous structure of the alloy to such an extent that it does not withstand the high temperatures (approximately 500.degree. C. or above) involved in glass bonding.
In an alloy film that contains fine crystals and is principally made of iron, such as an Fe-C or Fe-Si alloy film, the crystals can grow at high temperatures and deteriorate the film's soft magnetic characteristics, and therefore the film is not suitable for glass bonding.
When a magnetic head is produced using a conventional Co-Ta-Hf or other Co-M type noncrystalline soft magnetic film (wherein M represents one or more than one of the elements including Ti, Zr, Hf, Nb, Ta, Mo, V and W), the process of glass-bonding can give rise to a diffusive reaction involving oxygen on the interface of the core halves and the soft magnetic film, leading to degraded magnetic characteristics at the interfacial area of the product. More specifically, since M (such as Ta and Hf) contained in the soft magnetic film has a strong affinity for oxygen, some of the oxygen atoms contained in the ferrite of the magnetic core halves diffuse and cause changes in the composition of the ferrite due to a deficiency of oxygen and, accordingly, degradation of magnetic characteristics. A magnetically degraded area along the soft magnetic film eventually comes to form pseudo-gaps which contributes to degradation of the performance of the magnetic head, including an increased level of noise generation.